Putting added control onto your systems has never been easier. Just use Taco’s PC700 series of Power Controls along with any Taco Expandable Relay Unit (-EXP model). There are no complex wiring diagrams. Simply plug the interface cable directly into the expandable relay and attach the supplied sensors. That's it. By controlling the supply water temperature based on the outdoor temperature, the heat lost from the building is matched by the heat input to the building. You also optimize firing cycles of the boiler to increase comfort and provide energy savings. With the PC700 Power Control’s ease of installation and full diagnostic capabilities, you can simply and easily upgrade any system. In addition, you can use Taco Power Controls in parallel with the PC600 Series PowerPort Cards to further enhance total system operation.